This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The long-term goal of this project is to further understand the molecular mechanisms of gating in voltage-dependent channels, by focusing on the analysis of K+ channel gating in KcsA and KvAP. Analysis of the molecular identity of the pH sensor in the prokaryotic potassium channel KcsA identified several key mutants that stabilized the KcsA inner bundle gate in the fully open conformation at neutral pH, a fact that makes possible the crystallographic analyses of KcsA in a variety of functional states. Additional mutations in the selectivity filter were designed towards the determination of a fully conductive and an inactivated form of the channel and the probing of modal gating events.